1. Field of the Invention
The invention relates to the fields of polymer chemistry and polymer processing and relates to a device for the continuous modification of polymers in the flowable state by electron radiation that can be processed into molded articles or semifinished products before, during and after modification.
2. Description of Background Information
Electron irradiation today, both in the bench scale as well as in industrial application, is a very efficient method for modifying the structure and properties of polymers and plastics. [IAEA-TECDOC-1386: Emerging Applications of Radiation Processing. Proceedings of a Technical Meeting held in Vienna, 28-30 Apr. 2003; A. Heger: Technologie der Strahlenchemie von Polymeren. Hanser, Munich, Vienna 1990; M. Dole: The Radiation Chemistry of Macromolecules. Academic Press, Inc., New York, 1972]. The polymeric materials to be modified are thereby in the solid state before, during and after electron irradiation.
In the meantime, laboratory tests have shown that electron irradiation of polymers in the flowable state, i.e., in the melted state (and thus at increased temperatures), can lead to novel modification effects [T. Seguchi: Radiation and Physics and Chemistry 57 (2000) 367-371; A. Oshima et al.: IRaP2004-6th, International Symposium on Ionizing Radiation and Polymers, Sep. 25-30, 2004, Houffalize, Belgium; G. Wu et al.: Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 37, 1541-1548 (1999); K. Takashika et al.: Radiation Physics and Chemistry 55 (1999) 399-408; U. Lappan et al.: Nuclear Instruments and Methods in Physics Research B: 185 (2001) 178-183, M. Stephan et al.: MODES T2004, 3rd International Conference on Polymer Modification, Degradation and Stabilization, August/September 2004, Lyon, France; M. Stephan et al.: 11 th International Conference on Polymeric Materials 2004, Sep. 29.-Oct. 1, 2004, Halle/Saale, Germany 4-10].
For the laboratory-sized implementation of melt irradiation of this type, special irradiation vessels were built [DE 199 30 742 A1; DE 101 51 823 A1], with which a batch method is possible. However, with this arrangement the melting of the polymers occurs before and separately from the electron irradiation. That is, after the complete melting of the polymer sample, it is thereby irradiated inside an irradiation vessel. During the irradiation, the polymer sample is transported once or several times under the electron beam until the desired radiation dosage has been achieved. Subsequently, the electron accelerator is switched off and the polymer sample, now solidified again, can be removed from the irradiation vessel. However, this batch method is unsuitable for the industrial implementation of a melt irradiation.
Furthermore, a method for the continuous coating of electric cables with cross-linked polyethylene has been described in JP 53143796. As disclosed in JP 53143796, a metallic conductor as the core is guided downwards by a capstan and encased in a polyethylene melt produced in an extruder. From there, the coated conductor is guided downwards in a separate container, in which an electron irradiation is carried out under nitrogen atmosphere. However, due to the process control and device arrangement, the polyethylene coating of the metallic conductor is no longer in a flowable state at the time of the electron irradiation. As such, the application of this technology to other uses and manufacturing processes is not possible either.
U.S. Pat. No. 4,525,257 discloses a method for producing long-chain branched linear row-density polyethylene (LLDPE) by ionizing radiation, wherein the irradiation of the LLDPE also takes place as polymer melt in the extruder or during extrusion. However, the disadvantage is that devices for realizing this method are not disclosed.
A method for producing cross-linked polyethylene by irradiation using UV-light and an irradiation device is known from EP 0 490 854 B1. As disclosed by EP 0 490 854 B1, the irradiation device comprises an extruder with a forming device and a cover, within which a UV lamp is located. The hot, not yet solidified polyethylene melt is guided through on a transport belt inside the cover under the UV lamp and cross-linked thereby. However, this device is unsuitable for an irradiation with accelerated electrons, in particular, for reasons of radiation safety.